a) Field of the Invention
The present invention relates to a semiconductor memory based upon a new operation principle. Dynamic random access memories (DRAMs) are known as typical semiconductor memories. One bit data is stored in one memory cell of DRAM which is constituted of one MISFET and one capacitor. DRAMs having ultra fine memory cells and a high capacity are under development. Semiconductor memories capable of realizing a still larger capacity are still desired.
b) Description of the Related Art
A flash memory has drawn attention as semiconductor memories capable of realizing a larger capacity. The flash memory is suitable for realizing a larger capacity because one memory cell is constituted by only one MISFET.
Data is stored in a flash memory by injecting carriers into a floating gate electrode of a floating gate type FET. In order to retain carriers injected into the floating gate electrode, the thickness of an insulating film between the floating gate electrode and the channel region is set to about 8 nm. Carriers are injected via this insulating film into the floating gate electrode by applying a high voltage across the channel region and floating gate electrode. As a high voltage is applied between them, carriers are injected into the floating gate electrode by the Fowler-Nordheim tunneling (FN tunneling) phenomenon.
A voltage of about 10 to 20 V is required in order to inject carriers into the floating gate electrode by the FN tunneling phenomenon. It is therefore difficult to lower the voltage and reduce power consumption.